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CCRI J. Bernardini1 High Throughput (HT) and 802.11n Module-10B Jerry Bernardini Community College of Rhode Island.

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Presentation on theme: "CCRI J. Bernardini1 High Throughput (HT) and 802.11n Module-10B Jerry Bernardini Community College of Rhode Island."— Presentation transcript:

1 CCRI J. Bernardini1 High Throughput (HT) and 802.11n Module-10B Jerry Bernardini Community College of Rhode Island

2 Presentation Reference Material CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter-18 802.11n Demystified Companion Guide, Xirrus Inc USING MIMO-OFDM TECHNOLOGY TO BOOST WIRELESS LAN PERFORMANCE TODAY - DATACOMM RESEARCH COMPANY 6/30/2015Wireless Networking J. Bernardini2

3 802.11 Summary Characteristics CCRI J. Bernardini3 ProtocolRelease Date Op. Frequency Throughput (Typ) Data Rate (Max) Modulation Technique Range (Radius Indoor) Depends, # and type of walls Range (Radius Outdoor) Loss includes one wall 802.11a19995 GHz23 Mbps54 MbpsOFDM~35 Meters~120 Meters 802.11b19992.4 GHz4.3 Mbps11 MbpsDSSS -CCK~38 Meters~140 Meters 802.11g20032.4 GHz19 Mbps54 MbpsOFDM & DSSS~38 Meters~140 Meters 802.11n June 2009 (est.) 2.4 GHz 5 GHz 74 Mbps248 MbpsOFDM MIMO~70 Meters~250 Meters CCK-Complementary Code Keying OFDM-Orthogonal Frequency Division Multiplexing DSSS-Direct Sequence Spread Spectrum MIMO-Multi-Input Multi-Output

4 802.11n Requirements Backward compatible with 802.11abg Higher throughput than 802.11abg Mixed mode operation CCRI J. Bernardini4

5 Review 802.11g Protection Before an 802.11g client can transmit to an 802.11g AP it must reserve the medium. Must transmit so 802.11b will understand. Two Protection Methods – CTS-to self at 802.11b modulation (slow Clear to Send) – RTS-CTS at 802.11b modulation CTS-to-self is more efficient but may not be seen by hidden-node RTS-CTS is more reliable but has more overhead Both Methods dramatically reduce the 802.11g throughput CCRI J. Bernardini5

6 802.11b/g Mixed Mode Operation CCRI J. Bernardini6 AP 802.11g Station80 2.11g Station80 2.11b 1-Slow CTS 2-Slow CTS 3-Fast Data 2-Slow CTS

7 Protection Throughput Effect Technology Transactions per second Mbps of TCP payload throughput Transactional speed relative to 802.11b 11b, 11 Mbps4795.61.0 11a, 54 Mbps2,33627.34.9 11g, 54 Mbps/no protection 2,33627.34.9 11g, 54 Mbps/CTS-to- self protection 1,11313.02.3 11g, 54 Mbps/RTS/CTS protection 7508.81.6 Based on Matthew Gast, 802.11 Wireless Networks: The Definitive Guide CCRI J. Bernardini7

8 802.11g Conclusions 802.11g is significantly faster then 802.11b for all conditions 802.11b station associating with a 802.11g network drops throughput due to protection 802.11b station does not have to be active to reduce throughput (just associated ) Mixed 802.11b/g deployments are likely to be common for the foreseeable future Mixed 802.11b/a deployments will have higher throughput 802.11b/g/n will also have to provide protection CCRI J. Bernardini8

9 802.11n History In 2004 IEEE 802.11 Group-n formed to improve 802.11 standards 2009 802.11n draft Main objectives – Increase data rates and throughput – Operate in 2.4 GHz and 5 GHz bands 802.11n Draft defines High Throughput (HT) – Defines PHY and MAC enhancements – Can provide data rates up to 600Mbps Wi-Fi Alliance Certification CCRI J. Bernardini9

10 802.11n Draft Amendment Defines HT Uses Multiple-input Multiple-output (MIMO) OFDM MAC layer enhancements Backward compatible to 802.11abg 6/30/2015Wireless Networking J. Bernardini10

11 Wi-Fi Alliance Certification802.11n Most vendors say draft 2.0 software can be upgraded to 802.11n final Two spatial stream support-mandatory Two spatial receive stream support-mandatory A-MPDU and A-MSDU support- mandatory Block ACK support-mandatory Dual Band support-optional 40 MHz band support-optional Greenfield support –optional Short guard interval-optional Concurrent 2.4 GHz and 5Ghz--optional 6/30/2015Wireless Networking J. Bernardini11

12 MIMO Multiple-input Multiple-output (MIMO) Takes advantage of multipath Multiple radios and antennas CCRI J. Bernardini12 Transmitter x Receiver MIMO Tx Rx MIMO 2 3 2x3 3 3 3x3 4 4 4x4

13 Antenna Beamforming and Diversity 6/30/2015Wireless Networking J. Bernardini13 Beamforming (beam steering) employs two transmit antennas to deliver the best multipath signal Diversity (receive combining) uses two receive antennas to capture the best multipath signal

14 Multi-Antenna Systems not the Same 6/30/2015Wireless Networking J. Bernardini14 Multi-antennas beam steering/diversity approach, only one signal is sent over the channel. MIMO uses multiple transmitters, receivers and antennas to send multiple signals over the same channel, multiplying spectral efficiency.

15 MIMO and Multi-path – Normally when a signal is transmitted from A to B the signal will reach the receiving antenna via multiple paths, causing interference. – MIMO uses this multipath propagation to increase the data rate by using a technique known as spatial division multiplexing. – The data is split into a number of spatial streams and these are transmitted through separate antennas to corresponding antennas at the receiver. – Doubling the number of spatial streams doubles the raw data rate, enabling a far greater utilization of the available bandwidth. – The current 802.11n standard allows for up to four spatial streams. 6/30/2015Wireless Networking J. Bernardini15

16 Spatial Multiplexing (SM or SDM) MIMO employs multiple independent radio transmitter-receiver pairs Radio pairs send independent signals Transmitter antennas spaced by half-wave length or more – insuring different paths Each independent signal is a spatial stream Spatial streams are combined at the access point Referred to as: – Spatial Multiplexing (SM) or – Spatial Diversity Multiplexing (SDM) 6/30/2015Wireless Networking J. Bernardini16

17 MIMO Diversity Increasing the number of receiving antennas can improve overall signal to noise Pre-802.11n used switched diversity to select best multipath signal Increasing antennas (3 or 4) increases the receiver choice for a “good” signal MIMO maximal ratio combining (MRC) allows for additive effective of multipath signals – increasing signal to noise ratio 6/30/2015Wireless Networking J. Bernardini17

18 Transmit Beamforming (TxBF) 802.11n optional feature Multiple transmitter antennas “focus” the signal to a receiver Used by radar; phased-array antenna systems Transmitter is the beamformer Receiver is the beamformee Feedback from the beamformee allows the beamformer to adjust the antennas and signal to improve SNR 6/30/2015Wireless Networking J. Bernardini18

19 802.11n HT Channel Technology 802.11n uses OFDM (just as 802.11ag) 802.11n has option to use 20 MHz and 40 MHz channels 802.11n can use can combine channels for Channel Bonding 802.11n can use variable Guard Interval (GI) 802.11n can use various Modulation and Coding Schemes (MCS) CCRI J. Bernardini19

20 Non-HT and HT Channels (clause 20) 802.11ag use 20 MHz OFDM channels Each channel are made of 52 subcarriers – 48-subcarriers transmit data – 4-subcarriers transmit pilot tones for transmitter-receiver calibrations 802.11n can use either 20 MHz or 40 MHz channels Each HT 20 MHz channel has 56 subcarriers – 52-subcarriers transmit data – 4-subcarriers transmit pilot tones for transmitter-receiver calibrations Each HT 40 MHz channel has 114 subcarriers – 108-subcarriers transmit data – 6-subcarriers transmit pilot tones for transmitter-receiver calibrations 6/30/2015Wireless Networking J. Bernardini20

21 Channel Bonding 40 MHz channels are formed by bonding two 20MHz channels When bonding two channels there no need for a guard band 5 GHz UNNI band allows twenty three 20 MHz channels to be bonded 2.4 GHz ISM band allows only one bonding of two 20 MHz channels (only 3 non-overlapping channels) 6/30/2015Wireless Networking J. Bernardini21

22 Channel Bonding 6/30/2015Wireless Networking J. Bernardini22

23 Guard Interval (GI) Digital Symbol is a collection of bits If the bits overlap Inter-symbol Interference (ISI) is experienced 802.11ag uses a 800 ns guard interval between symbols 802.11n can use a 800 ns or 400 ns guard interval between symbols 400 ns GI improves throughput by 10% The 400 ns GI should only be used in a “good” RF environment 6/30/2015Wireless Networking J. Bernardini23

24 Modulation and Coding Schemes (MCS) 802.11n defines data rates as Modulation and Coding Schemes (MCS) MCS are based upon – Modulation technique (BPSK, QPSK, 16-QAM, 64-QAM) – Spatial streams (1, 4) – Channel size (20 MHz, 40 MHz) – Guard Interval (400 ns, 800 ns) 802.11n requires Eight mandatory 20 MHz MCSs Total of 78 MCSs Data rates vary from 6.5 Mbps to 600 Mbps 6/30/2015Wireless Networking J. Bernardini24

25 HT PHY and MPDU 802.11 frame is a MAC Protocol Data Unit (MPDU) The payload is the MAC service Unit (MSDU) (layer 7- 3 data) MPDU is made up of the header and body At the PHY layer is the Physical Layer Protocol Data Unit (PPDU) PPDU = MPDU + PHY preamble-header 802.11n defines three PHY preamble-headers Legacy format, HT Mixed, HT Greenfield CCRI J. Bernardini25

26 HT PPDU Formats Non-HT Legacy – Mandatory for 802.11n – Only 20 MHz channels – Same format as 802.11ag HT Mixed – Two part preamble – First part can be decoded by 802.11ag – Second part can not be decoded by 802.11ag HT Greenfield – Preamble can not be decoded by 802.11ag – Can use both 20 MHz and 40 MHz channels 6/30/2015Wireless Networking J. Bernardini26

27 HT MAC CCRI J. Bernardini27

28 HT Operation 20/40 Channel Operation – Legacy 802.11 communication using 20 MHz only – 802.11n can use 20MHz or 40 MHz HT protection Modes – Four modes – Mode 0, 1, 2, 3 Dual-CTS protection – Send both legacy and HT RTS/CTS combinations Phased Coexistence Operation (PCO) – Time slices between 20MHz or 40 MHz channel usage CCRI J. Bernardini28

29 Through Put Comparison 6/30/2015Wireless Networking J. Bernardini29

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